1. Field of the Invention
The present invention relates to the processing of digitized images and especially to systems designed to reduce the throughput of digital data needed for the storage or transmission of these images.
The encoding of color digital images at a low throughput rate requires a high data reduction ratio: for example, if a throughput rate of 10 M bits per second is sought, for a digital image source delivering data at 140 m bits per second, the data reduction rate is then 14.
2. Description of the Prior Art
A known method uses an encoder/decoder that performs an orthogonal transformation to obtain compression rates of this type. But a compression rate of this type creates faults in the images in certain circumstances.
These faults may be the following:
the boundaries of the blocks become visible in the uniform zones of the image;
visible oscillations occur at sharp, isolated transitions;
faults in restitution of data also become visible in the dark zones of the image.
An object of the invention is a method and corresponding device to reduce these faults through a filtering of blocks of images, adapted to the encoding conditions.